Especially the part about non-owned data was lacking, with basically no
information about what are offset-only attributes and fields actually
good for.
Instead of saying "which is not supported" in each assert, which is
vague and might imply that "it eventually will be supported", document
the actual reason in a single place, which is the MeshAttributeData docs.
Given the recent issues with vertex data with size over 4 GB, I feel
this limit might get hit soon as well. So far GPUs don't support vertex
counts larger than 32 bits, so storing them in a 32-bit number matches
the limitation there. Also, a vertex is usually at least 6 bytes (for
3-component positions quantized into 16-bit ints), thus a mesh hitting
this limit would be 24 GB in size. Which fits only on the beefiest
contemporary GPUs.
However I imagine the limit might get raised eventually, for example to
support a use case of a huge sparse mesh where only sub-parts of it are
drawn, and the sub-parts have counts that fit into 32 bits.
This is the first builtin array attribute, with one of the objectives
being an ability to support an arbitrary count of per-vertex weights in
a single contiguous attribute without the complexity of having to go
through several four-component attributes.
On the shader side it still needs to get cut into at most four
components per attribute, but there's no reason for such limitation to
get propagated here as well.
Co-authored-by: Vladimír Vondruš <mosra@centrum.cz>
I'm not sure why this restriction was there as nothing was preventing
them from being used. The attribute is only accessible through the
typeless attribute(), which gives back
`Containers::StridedArrayView2D<const char>` with second dimension size
being set to the full stride. And there it doesn't matter if the format
is an array or not.
This will be useful for joint IDs and weights, for example doing crazy
things like packing the IDs into an array of 8 4-bit numbers, saving
half the memory compared to the smallest builtin representation using
UnsignedByte[8].
The MeshData and SceneData find APIs had the complexity documented, do
the same for MaterialData too. Plus cross-link this API from
hasAttribute() / hasField() so it's easier to find.
I realized those are too annoying when writing a glTF exporter which
contains a lot of switches over enums. And as further shown by the diff,
those were only inflicting additional pain in *all* switch statements,
nothing else, no other added value. And everywhere else the helpers are
the designated way to deal with those, so there's no point in having an
explicit enum value denoting start of a "custom range".
It wasn't even any convenient to have it in the enum, as the extra
effort needed for casting actually made it *exactly* the same length as
if I'd just use a separately-defined constant.
This mirrors what's done already for implementation-specific vertex
formats, thus:
* Ability to construct the classes without tripping up when trying to
check for type size in various asserts
* Providing a zero-size type-erased access in indices() and
mutableIndices()
* Disallowing typed and convenience access
The type is now extended to 32 bits. In the GL and Vk libraries it means
one can now do things like
MeshIndexType type = meshIndexTypeWrap(GL_UNSIGNED_BYTE);
and passing that to GL::Mesh or Vk::Mesh will cause it to use the value
directly, instead of doing a mapping from a generic type. The *real* use
case for this is however to allow custom index buffer representations in
Trade::MeshData. Support for that will be hooked up in the following
commit.
Also not something the classic GPU vertex pipeline can handle, but
useful for other scenarios. Subsequently a support for array indices
will be added, allowing to directly represent for example OBJ files,
where each attribute has its own index buffer.
This is not something the classic GPU vertex pipeline can handle
(except maybe Vulkan, which can handle zero strides for instanced
attributes?), but useful for other scenarios. This means existing code
needs to be aware of and handle the new corner case.
This took me quite a while to realize -- not always it's desirable to
have the original layout unconditionally preserved, especially if for
example filtering a MeshData to just a subset of attributes.
Looking at the snippets, these seem to have been written back when there
was no builtin shaders yet, it seems, not to mention
MeshTools::compile(), Trade::MeshData or any of the other high-level
APIs. Rather overwhelming to just throw huge code snippets at the user,
explaining a workflow with a custom-made mesh that's going to be drawn
with a custom-made shader, which is like level 999 of using the GL
library.
It was rather discouraging to start "Basic usage" with a boring-ass long
snippet. On the other hand showing just compile() first would lead
people to think it's all some opaque magic, so trying to balance that a
bit.
Also why the hell was the compile() snippet showing the horrendous GL
way of specifying attribute formats? This is not great either but at
least not redundant.
Those have 3 pointers at least, my limit for passing by value is trivial
copyability and two pointers. I hope that reflects the actual HW at
least vaguely, heh.
Long ago, during one of the few initial MeshData iterations. there was
no VertexFormat, but rather Trade::MeshAttributeType. I managed to get
rid of it mostly, except this place.
Vladimír Vondruš